Impact of extended refrigerated storage and freezing/thawing storage combination on physicochemical and microstructural characteristics of raw whole and skimmed sheep milk

The impact of freezing (1 month + thawing at 7 or 25 °C) and extended refrigeration (4 days, 7 °C) on physicochemical and microstructural characteristics of raw whole and skimmed sheep milk were assessed. Refrigerated storage resulted in higher sedimentation and creaming (whole milk), possibly due to proteases and agglutinins. Freezing/thawing processes in whole milk increased the particle size and creaming when samples were thawed at 7 °C. Skimmed milk showed an increase in buffering capacity and a reduction in soluble calcium immediately after thawing at 25 °C, suggesting that although the changes in fat are the main alterations caused by slow freezing of sheep milk, minor changes in saline balance can occur. An evaluation of the results showed that frozen and thawed milk in domestic equipment (commonly found in smallholdings) alter the milk microstructure, and it is therefore preferable to use extended refrigeration to accumulate the milk before dairy production.     

The influence of storage temperature and storage time on color stability,retail properties and case-life of retail-ready beef

Steaks from three different muscles were either vacuum or carbon dioxide packed and stored for up to 24 weeks at three different storage temperatures (−1.5, 2, or 5 °C). Following storage, they were displayed for up to 30 h. CIE color coordinates, the oxidative states of myoglobin and pH were measured and muscle color, surface discoloration, retail appearance, and odor were evaluated prior to storage and during display (0, 1, 2, 4, 6, 24 and 30 h), and/or immediately prior to and following display. Prior to display, pH was negatively related to duration of storage, and samples stored at −1.5 °C had the highest and samples stored at 5 °C, had the lowest pH. Perception of muscle color was influenced by duration of storage and display, but lower storage temperatures appeared to produce a stabilizing effect. Both lightness of muscle color and deoxymyoglobin content were apparently not influenced by storage temperature or duration of storage or display. Both oxymyoglobin (OMB) and redness, as defined by CIE a* values, were lost progressively during storage and display, but this loss was progressively lower as storage temperature decreased. Yellowness of muscle color, as defined by CIE b* values, generally decreased as storage was prolonged, and this decrease was observed more quickly at higher storage temperatures. Surprisingly, b* values were not related to duration of display. Both surface discoloration and metmyoglobin (MMB) content increased progressively during storage and display. Samples stored at 5 °C displayed the most surface discoloration, while samples stored at −1.5 °C contained the least MMB and displayed the least surface discoloration. Retail appearance deteriorated progressively during storage in all samples stored at 2 and 5 °C and in samples stored at −1.5 °C, which were displayed for at least 24 h. Retail appearance also deteriorated progressively during display in samples stored at −1.5 and 2 °C for three weeks or longer and in samples stored at 5 °C for 0 to 15 and 24 weeks. In unstored samples, samples to be stored at −1.5 °C generally received the lowest retail appearance scores, but after prolonged storage and display, samples stored at −1.5 °C received higher retail appearance scores than samples stored at 5 °C, particularly when samples were stored for 12 weeks or longer and displayed for 1 h or more. Odor deteriorated progressively during storage when measured both prior to display and after 30 h of display. In samples stored for three weeks or longer, samples stored at −1.5 °C generally received the lowest odor scores and were perceived to have the least prevalent off-odors. Samples stored at −1.5 °C maintained a retail case-life of 30 h, when stored for up to 17 weeks, while samples stored at 2 and 5 °C maintained a retail case-life of 30 h, when stored for only eight and seven weeks, respectively. Consequently, storage life can be more than doubled by storage at subzero temperatures (−1.5 °C).     

Properties of low-fat stirred yoghurts made from high-pressure-processed skim milk

Physical properties of stirred yoghurt made from reconstituted skim milk that was high-pressure (HP)-treated at 100, 250 or 400 MPa, at 25, 70 or 90 °C, for 10 min, prior to inoculation with yoghurt cultures, were studied; portions of milk HP-treated at 25 °C were also heat-treated at 90 °C for 10 min before or after pressure treatment. Control yoghurts were made from skim milk given a heat treatment at 90 °C for 10 min. Fermentation time was not affected by treatment applied to the milk. HP treatment of skim milk at 25 °C, before or after heat treatment, gave stirred yoghurts of similar viscosities to that made from conventionally heat-treated milk. Lower viscosities were obtained when stirred yoghurts were made with milk HP-treated at elevated temperatures. A model is proposed to correlate properties of yoghurt with HP/heat-induced changes in interactions and structures of protein in the milk samples.Industrial relevanceTo meet end user expectations, the dairy industry needs to diversify its product range by tailoring specific functionalities. To meet these expectations, new processing methods such as high-pressure processing are of interest for their potential to achieve specific and/or novel functionalities and/or improve efficiencies, including reduced chemical and water use. In this paper, an investigation of the use simultaneous pressurization and heating of milk before the manufacture of stirred yoghurt is presented.     

Effects of high pressure treatment on physicochemical characteristics of fresh sea bass (Dicentrarchus labrax)

The effects of high pressure (HP) treatment (pressure: 220–250–330 MPA; holding time: 5 and 10 min; temperature: 3, 7, 15 and 25°C) on physicochemical characteristics (colour, thiobarbituric acid, trimethylamine nitrogen values) of fresh sea bass fillets were investigated. HP-treated sea bass fillets had higher lightness (Hunter L*) values than untreated sea bass fillets; the magnitude of changes increased with treatment pressure. HP-induced changes in colour generally imparted a cooked sample. The TBA value of HP treated sea bass samples (except 220–330 MPa, 3°C for 5 min) were found to be insignificant (P > 0.05) or significantly (P < 0.05) lower than the untreated samples. TMA-N content of HP treated at 220–250–330 MPa, 3–7–25°C for 10 min sea bass samples were found to insignificant according to the untreated samples. The results obtained from this study showed that the quality of high pressure treated sea bass is best preserved at 220 MPa, 25°C for 5 min.     

Oxidative stability of ultra high temperature milk enriched in conjugated linoleic acid and trans-vaccenic acid

Milk naturally enriched in conjugated linoleic acid (CLA) and trans-vaccenic acid (TVA) was ultra high temperature (UHT)-treated at 125–145 °C for 2–20 s and stored at 4 and 25 °C for up to 120 d. The oxidative stability of treated enriched milk was evaluated in terms of changes on the contents of CLA and TVA, dissolved oxygen, hydroperoxides, thiobarbituric acid reactive substance (TBARS) and formation of volatiles. After UHT treatment, more than 78% of CLA and 87% of TVA remained. After 15 d of storage at 25 °C, the CLA and TVA were relatively stable with values in the range of 67–75 and 63–73%, respectively. During storage, CLA oxidized faster than TVA, independently of the UHT treatment and storage conditions. Heptanal was the most abundant volatile resulting from UHT processing and a potential suitable marker for heat treatment of milk rich in CLA and TVA.     

Effects of high pressure treatment on physicochemical characteristics of fresh sea bass (Dicentrarchus labrax)

The effects of high pressure (HP) treatment (pressure: 220–250–330 MPA; holding time: 5 and 10 min; temperature: 3, 7, 15 and 25°C) on physicochemical characteristics (colour, thiobarbituric acid, trimethylamine nitrogen values) of fresh sea bass fillets were investigated. HP-treated sea bass fillets had higher lightness (Hunter L*) values than untreated sea bass fillets; the magnitude of changes increased with treatment pressure. HP-induced changes in colour generally imparted a cooked sample. The TBA value of HP treated sea bass samples (except 220–330 MPa, 3°C for 5 min) were found to be insignificant (P > 0.05) or significantly (P < 0.05) lower than the untreated samples. TMA-N content of HP treated at 220–250–330 MPa, 3–7–25°C for 10 min sea bass samples were found to insignificant according to the untreated samples. The results obtained from this study showed that the quality of high pressure treated sea bass is best preserved at 220 MPa, 25°C for 5 min.     

Nutritional changes in maize (Zea mays) during storage at three temperatures

Nutritional changes in maize grains stored at 10, 25 and 45 °C for 6 months were studied. Significant decrease in pH and increase in titratable acidity was observed during storage of maize grains at 25 and 45 °C. Moisture contents of maize grains decreased by 25% at 25 °C and 38% at 45 °C after six months of storage. Total soluble sugars increased by 10.7% at 10 °C and 17.3% at 25 °C, whereas a 39.5% decrease was observed after 6 months storage at 45 °C. Total available lysine and thiamine contents in maize grains decreased by 13 and 9.26% at 25 °C, 16 and 20.4% at 45 °C, respectively, after 6 months of storage. Protein digestibility decreased by 5.19 and 9.0% at 25 and 45 °C, respectively, whereas decrease in starch digestibility was 9.86% at 25 °C and 15.1% at 45 °C on storage of maize grains for 6 months. However, no significant nutritional changes occurred during storage of maize grains at 10 °C.     

Fourier transform infrared spectroscopy analysis of physicochemical changes in UHT milk during accelerated storage

The feasibility of using Fourier transform infrared spectroscopy (FTIR) to detect heat induced conformational rearrangements of proteins, protein–protein and protein–lipid interactions was studied with accelerated shelf-life protocols. Ultra-high temperature treated whole (WM) and skim milk (SM) were stored at 20, 30, 40 and 50 °C for 28 days. The changes leading to increased sedimentation in SM and WM at higher temperatures (≥40 °C) were observed during first 14 days of the storage period. Milk samples stored at 40 and 50 °C showed marked changes in the bands corresponding to conformations of milk lipids and formation of intermolecular β sheet of proteins, indicating protein–lipid interactions and aggregation. Dried sediment contained fat confirming protein–lipid participation in the sedimentation. FTIR was also able to detect changes that led to increased sedimentation in SM at temperatures lower than 40 °C, but only after 28 days.     

Effect of storage conditions on nutritional quality and color characteristics of quinoa varieties

To maintain grain quality and prevent loss, effective storage systems are required. The aim of this study was to evaluate the effects of storage duration (0, 60, 120, 180, 240, 300, 360 days) and temperature (4, 10, and 25 °C) on proximate and nutritional components, and color properties of Mint Vanilla and Titicaca quinoa varieties. The results showed that the increase in storage duration and temperature leads to changes in the grain moisture, protein and ash contents, nutritional component and color properties. There was an increase in ash content at 25 °C, moisture content at 10 and 25 °C, and protein content at 4 °C in the stored grains compared with the grains on the initial of storage for Mint vailla variety. Whereas, there was an decrease in ash and protein content for all the temperature at the end of 360 days storage for Titicaca variety. Overall, there was a decrease (except Fe, Zn, Co, Ni, Cd and Pb) in the nutritional component of both quinoa varieties. L1, H° and WI values decreased, and a1, b1 and C1 values increased as a function of storage duration and temperature and showed some temperature-dependent degradation for both quinoa varieties.     

Effect of dissolved carbon dioxide on the sonocrystallisation and physical properties of anhydrous milk fat

The effects of dissolved CO₂ (0–2000 ppm) coupled with ultrasound (US; 20 kHz) on the physical properties of anhydrous milk fat (AMF) were examined. Carbonated AMF was sonicated at 28 °C for 5 s at various amplitudes and subjected to isothermal (28 °C) and non-isothermal (cooling from 28 to 5 °C) crystallisation conditions. AMF microstructure, thermal properties and hardness were evaluated after 48 h of storage. In general, carbonated AMF samples treated with the same US amplitude exhibited a slight decrease in endset-melting temperature, smaller fat crystals with denser fat crystal network. Dissolved CO₂ caused harder texture of sonicated AMF at 25 °C. However, when carbonated + sonicated AMF samples was stored at 5 °C, their texture appeared to be softer than that of the control sample. A protective effect of CO₂ against formation of primary oxidative products during 90 days of storage was evidenced in both non-sonicated and sonicated AMF.     

Effects of high-pressure and heat treatments on physical and biochemical characteristics of oysters (Crassostrea gigas)

Physical and biochemical changes in oysters following high-pressure (HP) treatment at 260 MPa for 3 min or heat treatment (cool pasteurisation (CP) at 50 °C for 10 min or traditional pasteurisation (TP) at 75 °C for 8 min) were investigated and compared to changes in untreated oysters. HP or TP oysters had higher (P < 0.05) pH values (6.49–6.58) than untreated or CP oysters (6.45–6.46). HP and heat treatment both modified the gross composition of oyster tissue. The protein content of HP-treated oysters (6.9%) was significantly (P < 0.05) lower compared to control or heat-treated oysters (7.9–9.1%). The moisture content of HP-treated whole oyster tissue (86.5%) was higher than that of heat-treated or untreated oysters (83.5–84.7%), but HP or CP treatments did not affect the salt content or water activity of oysters. However, all treatments increased Hunter L- (66.3–68.9) while decreasing a- (− 1.6 to − 2.4) and b- (15.8–14.5) values of oyster tissue; overall, HP treatment had less negative effects on tissue colour of oysters than thermal treatments. HP-treated, CP and TP oysters had higher shucking yields (15.5%, 12.5% and 2.6%, respectively) than untreated oysters. One significant advantage of HP treatment over heat treatment of oysters was that the former process opened the oyster and separated the muscle of the oyster from the shell.     

Sensory Quality of Nonfat Dry Milk after Long-Term Storage

Nonfat dry milk was stored under various conditions to determine the effects of temperature, packaging, atmospheric gases, and form of milk on the sensory quality of the stored product. Nonfat dry milk was significantly affected by storage temperature during long-term storage. Nonfat dry milk held at 32°C for 6 mo began to develop offflavors and by 24 mo was considered unacceptable when evaluated by a trained sensory panel. After 4-yr storage nonfat dry milk samples stored at 21°C were rated unacceptable by the panelists. Storage at 10°C resulted in minimal flavor changes in 52 mo. After 4-yr storage, nonfat dry milk samples stored in Polybags were statistically less acceptable than samples stored in cans. The form of milk (instant or regular) did not affect the length of time nonfat dry milk could be stored. Unacceptability of samples was due to an oxidized/stale flavor.     

Behaviour of Listeria monocytogenes and Staphylococcus aureus in sliced,vacuum-packaged raw milk cheese stored at two different temperatures and time periods

The behaviour of Listeria monocytogenes and Staphylococcus aureus in raw milk cheese slices packaged under vacuum was evaluated. Artificially contaminated 80-day ripened cheese was portioned, vacuum packaged, and then stored for 28 days at 4 °C and for 56 days at 10 °C. Bacterial counts were obtained before vacuum packaging and then weekly during storage. At the end of ripening, the initial L. monocytogenes count was 4.46 ± 0.89 log cfu g⁻¹; weekly bacterial counts remained substantially unchanged in the samples stored at 4 °C but decreased to 3.54 ± 1.54 log cfu g⁻¹ in those stored at 10 °C. The initial S. aureus count before vacuum packaging was 3.60 ± 0.78 log cfu g⁻¹; it then gradually decreased to 2.60 ± 1.32 log cfu g⁻¹ in the samples stored at 4 °C and to about 1.9 log cfu g⁻¹ in those stored at 10 °C.     

Proteolysis and storage stability of UHT milk produced in Turkey

The effect of raw milk quality (total and psychrotrophic bacterial and somatic cell counts, proteinase and plasmin activity) and UHT temperature (145 or 150 °C for 4 s) on proteolysis in UHT milk processed by a direct (steam-injection) system was investigated during storage at 25 °C for 180 d. High proteinase activity was measured in low-quality raw milk, which had high somatic cell count, bacterial count and plasmin activity. The levels of 12% trichloroacetic acid–soluble and pH 4.6-soluble nitrogen in all milk samples increased during storage, and samples produced from low-quality milk at the lower UHT temperature (145 °C) showed the highest values. Bitterness in UHT milk processed from low-quality milk at 145 °C increased during storage; gelation occurred in that milk after 150 d. The RP-HPLC profiles of pH 4.6-soluble fraction of the UHT milk samples produced at 150 °C showed quite small number of peaks after 180 d of storage. Sterilization at 150 °C extended the shelf-life of the UHT milk by reducing proteolysis, gelation and bitterness.     

Determination of the survival kinetics of Salmonella spp. on the surface of ripened raw milk cheese during storage at different temperatures

The aim of this study was to determine the survival kinetics of Salmonella enterica subsp. enterica in ripened raw milk cheese. Cheese samples inoculated with S. enterica subsp. enterica were stored at 5, 15 and 25 °C and analysed in terms of physico-chemical and microbiological characteristics. Three primary models were used to estimate the kinetic parameters of S. enterica subsp. enterica. The secondary Arrhenius model was used to establish the relationship between temperature and parameter α of the Weibull model. Additionally, prediction of S. enterica subsp. enterica survival as a function of storage temperature was made. S. enterica subsp. enterica growth was inhibited during storage, and bacteria survived for an extensive period of time at high number (60 day at 5 °C, 26 day at 25 °C). The storage temperature significantly influenced the inactivation rate of Salmonella in raw milk ripened cheese and proceeded faster at 25 °C compared to remaining storage temperature. Obtained results suggest that contamination by Salmonella in raw milk cheese might result in residual risk.     

Effect of calcium lactate and heat-shock on texture in fresh-cut lettuce during storage

Textural and microstructural changes in fresh-cut lettuce were analysed over 12 days storage. The vegetable was treated with 120 ppm chlorine and with 15 g/L calcium lactate at room temperature (∼18–20 °C) and at 50 °C (heat-shock). Texturometer analysis showed that samples washed with calcium lactate had significantly (p > 0.05) higher crispness values than samples washed with chlorine. However the use of 50 °C treatment (heat-shock) gave better textural properties at the end of storage and significantly retarded the softening process, being in agreement with the sensorial results. Cryo-SEM micrographs showed a loss of turgor (shrinkage) of the tissue cells in the samples washed with chlorine, effect not so evident in calcium lactate treated samples. The use of heat-shock in combination with calcium lactate reduced this phenomenon better than the other two treatments. Pectin methyl esterase (PME), enzyme related to textural changes, showed higher activity in samples treated with calcium lactate at 50 °C. The combination of calcium lactate and 50 °C washing temperature maintained objective and sensorial textural properties of fresh-cut lettuce better than the calcium lactate or chlorine washing treatments at room temperature.     

Counteracting Recontamination of Pasteurized Milk by Methylated Soybean Protein

Methylated soy protein (MSP) was evaluated as an antimicrobial agent that can counteract the potential post-pasteurization contamination of milk during a 30-day cold storage (4 °C) or 24-h room temperature storage (25 °C) as compared to its native form (SP). SP and MSP were added to buffalo milk at 0.5% (w/v) after pasteurization and before storage. Milk microbiological and chemical analyses were carried out either directly to follow the spontaneous microbial contamination or after artificial contamination with three pathogens (Escherichia coli O157:H7, Listeria monocytogenes Scott A, and Salmonella enterica subsp. enterica serovar Enteritidis PT4). Supplementation of milk samples with MSP (0.5%) significantly (p?<?0.05) and considerably inhibited the levels of the spontaneously proliferating bacterial counts, i.e., total viable and Enterobacteriaceae counts were inhibited by about 2.5 log CFU mL^?1, while psychrotrophic and pseudomonads counts were inhibited by 1.8 and 1.6 log CFU mL^?1, respectively, after 16 days of preservation at 4 °C. Similar trend of effects were also produced after 12–18 h of milk storage at 25 °C. MSP (0.5%) nearly hindered the proliferation of the three inoculated pathogens in pasteurized milk during 16 days of storage at 4 °C or 12–18-h storage at 25 °C. Based on milk acidity, SDS–PAGE pattern, and microbiological analysis, it is concluded that supplementation with MSP (0.5%) can prolong the shelf life of pasteurized milk from 6 to 16 days when stored under cold conditions and from 8 to 18 h under room temperature conditions.     

Changes in physicochemical characteristics of rice during storage at different temperatures

This study investigated the changes in the physicochemical properties of rice during storage at different temperatures. Milled rice stored at high temperatures showed higher fat acidity than rice stored at low temperatures. Although the moisture content of milled rice stored at 30 °C and 40 °C decreased below 15.5% (15.33% and 15.22%, respectively) after 1 month, adequate values were maintained with storage at 4 °C for 3 months (15.50%) and at 20 °C for 2 months (15.53%). Rice stored at low temperatures retained its white coloration, whereas low color retention values were obtained at higher storage temperatures. Peak viscosity increased during 4 months of storage and larger changes were found at higher storage temperatures. Breakdown decreased and setback increased with storage, regardless of storage temperatures. Storage at higher temperatures increased cohesiveness and hardness in compared with storage at lower temperatures. High temperatures also led to a decrease in adhesiveness with age. High temperatures (30 °C and 40 °C) significantly decreased all sensory values even after 1 month of storage. These results are similar to those obtained in an analysis of cooked rice texture. The results of this study indicate that storage temperature is an important factor affecting the physicochemical properties of rice. Short storage periods below room temperatures are recommended to maintain rice quality.     

Rheological Properties of Chymosin-Induced Skim Milk Gels as Affected by Milk Storage Time and Temperature

Fundamental dynamic rheological tests were used to measure the rigidity (|G*|) and viscoelasticity (tan δ) of gels made from skim milk samples that were (1) never cooled, (2) stored at 4°C, or 3) stored at 4°C and then rewarmed to 25°C. Milk cooled and held at 4°C prior to gel formation produced gels with lower |G*| and higher tan(δ) than fresh milk gels. Chilled milk samples that were rewarmed to 25°C for 16h prior to gel formation produced gels with rheological properties similar to fresh milk gels. The solubilization of β-casein during cold storage was hypothesized to be the cause of observed differences in gel rheology.     

Effect of storage temperature on rice thermal properties

Study on the gelatinization kinetics of rice showed that gelatinization process was divided into two steps: swelling of the amorphous region and disruption of the crystalline region. Higher temperature storage (37 °C) resulted in an increase in the breaking point temperature suggesting that energy for the disorder of these two regions of starch in rice stored at 37 °C was higher than the rice stored at 4 °C. Storage-induced changes in rice led to significant increases in DSC peak temperature (p < 0.05) and significantly broadened peak width (p < 0.01) for rice stored at 37 °C compared to rice stored at 4 °C. As the peak temperature of rice stored at 37 °C was not influenced by the “annealing” treatment in contrast with the increased peak temperature of rice stored at 4 °C after the “annealing” treatment, the results indicate that the ageing process (37 °C storage) has already re-ordered the rice grain structure and that the annealing process under these conditions has no further effect on starch thermal properties. Because starches isolated from rice grain stored at 4 °C and 37 °C had similar thermal properties, this implies that the effects of storage on thermal properties are associated with the interactions between starch and non-starch components following storage. The gelatinization endotherm shifted to a lower temperature (p < 0.01) and a narrowed peak width was achieved after cellulase and protease treatments of stored rice, which indicates that the changes in cell wall remnants and proteins are responsible for the changes in rice thermal properties during storage. Scanning electron microscopy was applied to visualize the treatments of cellulase and protease on rice.